1. Field of the Invention
This invention relates to a DC motor, and more particularly to a DC motor provided with a centrifugal governor device for controlling the speed of revolution of such motor.
2. Description of the Prior Art
Various types of DC motors provided with a governor device for controlling the speed of revolution have heretofore been proposed. Among these, a relatively popular type is that in which the governor switches of the governor device are designed to opened and closed by centrifugal force in a plane perpendicular to the axis of the rotary shaft of the motor. In a motor provided with such a governor device, however, the force acting on the governor switches is not constant and particularly so when the direction of revolution of the motor is changed, and this is a disadvantage in that the controlled speed of revolution cannot be made always constant irrespective of the direction of revolution of the motor. Also, the governor device has been disposed at a location spaced apart with respect to the armature coils in the axial direction of the rotary shaft and this has prevented reduction in size of the motor and also led to a disadvantage in that cumbersome procedures are involved in making connections between electrical parts during assembly of the motor. This last-mentioned disadvantage has particularly been pronounced in a motor wherein the governor device is disposed with respect to the armature coil on the opposite side from that side on which the rectifier is disposed and spark extinguishing electrical elements are connected between the segments of the commutator and between the governor switch contacts.
To eliminate the above-noted disadvantages which have existed in a motor provided with a governor device operable in the plane perpendicular to the axis of the rotary shaft, there has heretofore been proposed a motor provided with a governor device operable in a plane containing the axis of the rotary shaft. A first example of such motor is that in which three cylindrical weight members are inserted radially with respect to the rotary shaft and between coils comprising windings provided on three cores arranged symmetrically and radially and the rotary shaft is secured by means of resilient member with respect to the opposite side from that side on which the commutator is disposed. Screw members are threaded into the respective weight members from the back surfaces thereof and radially with respect to the rotary shaft. First silver contacts are joined to the tip ends of the screw members while second silver contacts are joined to the tip ends of conductor pieces exposed outwardly of the segments of the commutator. The second silver contacts are opposed to the first silver contacts. A second example is a motor in which one or more of the armature poles are auxiliary poles having no winding thereon. Such auxiliary poles are formed with holes parallel to the rotary shaft, in which holes are mounted governor switches having movable contacts and fixed contacts operable to open and close in a plane containing the axis of the rotary shaft.
Any of these motors heretofore proposed has involved special connections for the commutator and the armature core, which in turn has complicated the construction of the armature itself and thus offered various problems in practice.
For instance, in the above-mentioned first example of the motor, additional conductor pieces must be provided to the commutator segments and inconveniently, special connecting procedures are involved in connecting spark extinguishing electrical elements between the commutator segments and between the governor switches. In the second example of the motor, one or more auxiliary poles having no winding must be provided among the armature poles and holes must be formed through such auxiliary poles. Also, when there are three armature poles one of which provides the auxiliary pole, four special, dimensionally irregular, commutator segments including two smaller segments are required for connecting the governor switches and some special connecting method must be adapted between electrical parts.
All of the motors heretofore proposed are of special designs that will cause the prior art motors to be greatly reformed. This might lead to disadvantages such as much more complicated procedures of assembly and wiring, and higher cost of manufacture.